1985-1986 Honda ATC250R Shop Manual, Page 78Get this manual
CYLINDER HEADCYLINDERPISTON
Check the cylinder and piston for wear or damageClean carbon deposits from the exhaust port areaCAUTION
D; not damage the cylinder bore-]
NOTE Under racing conditions, the piston and rings should be replaced after 30 hours of runningAnd the piston pin and connecting rod small end bearing replaced after 30 hours of running